public function save( $post_id ) {

		if ( ! isset( $_REQUEST['lifterlms_meta_nonce'] ) ) {
			return -1;
		}
		if ( ! wp_verify_nonce( sanitize_text_field( wp_unslash( $_REQUEST['lifterlms_meta_nonce'] ) ), 'lifterlms_save_data' ) ) {
			return -1;
		}

		$order = llms_get_post( $post_id );
		if ( ! $order || ! is_a( $order, 'LLMS_Order' ) ) {
			return 0;
		}

		if ( ! current_user_can( 'edit_post', $post_id ) ) {
			return -1;
		}

		$fields = array(
			'payment_gateway',
			'gateway_customer_id',
			'gateway_subscription_id',
			'gateway_source_id',
		);

		foreach ( $fields as $key ) {

			if ( isset( $_POST[ $key ] ) ) {
				$order->set( $key, llms_filter_input_sanitize_string( INPUT_POST, $key ) );
			}
		}

		// Only allow editing the total (for the next recurrence) if this is a recurring order.
		if ( $order->is_recurring() && isset( $_POST['total'] ) && is_numeric( $_POST['total'] ) ) {
			$total = floatval( $_POST['total'] );
			$order->set( 'total', $total );
			$order->add_note( sprintf( __( 'Order total for future payments updated to %s.', 'lifterlms' ), $order->get_price( 'total' ) ) );
		}

		$this->save_remaining_payments( $order );

		return 1;
	}